This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
The present disclosure relates generally to ultrasonic pulse-echo caliper measurements using a downhole ultrasonic caliper. In particular, the present disclosure relates to a downhole tool using an ultrasonic caliper with multiple acoustic transducers for logging-while-drilling (LWD) and wireline logging applications.
Ultrasonic pulse-echo caliper measurements had been provided for more than 30 years in the oil field as the commercial wireline and logging-while-drilling (LWD) services. The ideas have been present since the late 1960's and the measurements usually involve already proven technologies. However, unlike the mechanical calipers commonly used in Wireline services, LWD ultrasonic pulse-echo measurements are based on a non-contacting echolocation method that is free from complex and costly mechanical system that often include expandable arms and associated mobile structures, and which may not be reliable for LWD application. Therefore, the majority of LWD tools uses non-contacting methods including ultrasonic measurements.
Ultrasonic pulse-echo measurements measure two-way transit time between an ultrasonic transducer and the borehole wall using another transducer as a transceiver. To convert the transit time to standoff or distance between the transducer and the borehole wall, the acoustic wave propagation velocity in well fluid is required (and which will be called “fluid acoustic velocity” or its reciprocal, “fluid acoustic slowness”, and replacing “fluid” by “mud” hereafter).
In conventional LWD tools, the fluid acoustic velocity was often estimated from formula that relates the acoustic velocity to fluid compositions (for example, density, type of mud such as water-base, oil-base and synthetic oil-base, oil/water ratio, amount of additives such as gelifiant, solid or soluble weighting agent for example, barite or salt) and environmental parameters (for example, pressure and temperature). In the actual logging environment, the fluid acoustic velocity may not be constant but dynamically varies due to localized depth or time-dependent mud compositions in more than kilometers of well length, mud flow, pressure and temperature, formation gas/fluid influx, and amount of cuttings. Measurement of fluid acoustic velocity is required for improving accuracy and reliability of the ultrasonic caliper measurements as well as robustness.
U.S. Pat. No. 3,502,169 (Chapman/Schlumberger, 1968) discloses a principle of a downhole imager, referred to as a sonic borehole televiewer, applicable to either cased or open hole utilizing ultrasonic pulse-echo amplitude measurements. The target application is for Wireline, however, it discloses pulse-echo amplitude referring to well azimuth using a magnetometer and cable depth.
U.S. Pat. No. 4,571,693 (Birchak/NL Indusctires, Inc, 1983) discloses a principle of downhole well fluid property measurement including the well fluid's acoustic velocity, utilizing an ultrasonic pulse-echo transducer. However, this technique is dedicated for property measurement, and does not permit pulse-echo caliper measurement.
U.S. Pat. No. 4,601,024 (Broding/Amoco Coorporation, 1981) discloses a principle of ultrasonic pulse-echo imaging technique utilizing energy, and is known as a borehole televiewer (BHTV), of which the concept is similar to the technique in U.S. Pat. No. 3,502,169. In these documents, nothing is claimed on transit time data usage or a caliper application.
U.S. Pat. No. 4,979,151 (Ekstrom et al/Schlumberger, 1987) discloses one possible embodiment of two ultrasonic pulse-echo transducers to estimate acoustic impedance and acoustic wave propagation for acoustic velocity for standoff measurement, using electromagnetic measurements correction for standoff. In this document, a transducer is also proposed that is dedicated for standoff measurement instead of borehole fluid property measurements.
U.S. Pat. No. 5,354,956 (Orban et al/Schlumberger, 1993) discloses a detailed structure of one possible ultrasonic pulse-echo transducer and multiple, preferably 2, transducers mounted on a drill collar at diametrically opposed positions for downhole standoff and caliper measurements, aiming LWD applications. The reference explains materials used in transducer assemblies, e.g., lead metaniobate as piezoceramic element, PEEK window, and tungsten-loaded rubber as backing. The reference also explains measurement methods including downhole electronics, signal processors, example waveforms and their interpretation methods. For mud acoustic velocity, Orban proposes the usage of a database that provides the most probable mud acoustic velocity at given pressure and temperature conditions. Note that the disclosure of U.S. Pat. No. 5,354,956 is incorporated herein in its entirety by reference thereto.
U.S. Pat. No. 5,341,345 (Waner et al/Baker Hughes Incorporated, 1993) discloses an LWD downhole caliper and mud acoustic velocity measurements method using two transducers, i.e., one mounted on the external and another mounted on the internal surfaces of a drill pipe. The internal transducer measures the acoustic velocity inside the pipe, which may be different from the acoustic velocity measured outside due to differences in composition (borehole fluid/gas influx and cutting presence) and temperature/pressure.
U.S. Pat. No. 5,640,371 (Schmidt et al/Western Atlas International, Inc., 1995) discloses a downhole ultrasonic transducer design utilizing multiple segmented piezoelectric elements focusing on phased array beam focusing application, which is different from sensitivity or signal amplitude gain taking the benefit of impedance matching.
U.S. Pat. No. 5,987,385 (Versamis et al/Dresser Industries, Inc., 1998) discloses a downhole imaging using pulse-echo amplitude, recorded using three pulse-echo transducers in an LWD tool with pressure and temperature sensors for amplitude correction, and a magnetometer to orient recorded values to well bore azimuth. Removal of source signal, i.e. averaged waveforms, is also disclosed. Note that the disclosure of U.S. Pat. No. 5,987,385 is incorporated herein in its entirety by reference thereto.
U.S. Pat. No. 6,038,513 (Versamis et al/Dresser Industries, Inc., 1998) disclosed an elliptical fitting of standoff values using three ultrasonic pulse-echo standoff values measured using structure shown in exemplary of the foregoing U.S. Pat. No. 5,987,385. Mud acoustic velocity estimation is based on a database method similar to the one claimed in the foregoing U.S. Pat. No. 5,354,956. Estimation of the long and short axes is discussed without detailing the method.
U.S. Pat. No. 6,618,322 (Gerogi/Baker Hughes Incorporated, 2001) discloses one single pulse-echo transducer to measure mud acoustic velocity and standoff by adding a partial wave reflector at controlled distance from the pulse-echo transducer, however, the reference does not appear to explain how to compensate a measured standoff for tool eccentering, since the main application is to compensate NMR measurements for standoff.
U.S. Pat. No. 6,466,513 (Pabon/Schlumberger, 2002) discloses another possible embodiment of ultrasonic pulse-echo transducer for LWD application. The reference also discloses mud acoustic velocity measurements adding two diametrically opposed transducers in the internal annulus of the BHA (Bottom Hole Assembly). Mud acoustic velocity measurements inside the pipe has similar limitation as the technique disclosed in the foregoing U.S. Pat. No. 5,341,345. Note that the disclosure of U.S. Pat. No. 6,466,513 is incorporated herein in its entirety by reference thereto.
U.S. Pat. No. 8,130,591 (Geerits/Baker Hughes Incorporated, 2008) discloses a mud acoustic velocity measurement technique similar to the one disclosed in the forgoing U.S. Pat. No. 6,466,513.
U.S. Pat. No. 8,260,554 (Morys/Halliburton, 2009) discloses a method to measure tool positions, i.e., azimuthal orientation and two dimensional position in plane normal to borehole axis, respectively using magnetometer and orthogonally oriented accelerometers. No mud acoustic velocity measurements are discussed.
U.S. Pat. No. 8,788,207 (Pei et al/Baker Hughes Incorporated, 2011) discloses borehole geometry and tool position using standoff data recorded using multiple pulse-echo transducers (exemplary 5) in multiple turns, using iterative polygon fitting method and minimization of error. No details are discussed for mud acoustic velocity estimation. Note that the disclosure of U.S. Pat. No. 8,788,207 is incorporated herein in its entirety by reference thereto.
U.S. Pat. Application Publication No. 2004/0095847 (Hassan et al/Baker Hughes Incorporated, 2002) discloses mud acoustic velocity measurement methods using pitch-catch and two single transducers offset along the radial direction of LWD tool. The pulse-echo technique enables real-time measurements of both acoustic wave propagation speed in downhole fluid and standoff measurements, however, limited in providing sufficiently robust and precise mud acoustic velocity and caliper measurement as it assumes the tool is in stationary position in the time interval in which two transducers are at the same position in the borehole. The second assumption, the minimum transit time at the moment of tool eccentering in borehole (or the transducer is fired toward borehole at known standoff at the time of eccentering), is not reliable enough.
Claimed techniques are limited as LWD tools that prone to present non-stationary tool motion, sometimes in the mode that tool rotation and revolution are synchronized and BHA transducer mounted section is not always contacting to the borehole wall. The transit time could be shorter than anticipated value as the borehole is not necessarily parallel to the BHA, and heavy metallic BHA start reaming the wall when they are eccentered and contacting wellbore surface unless the BHA and drill strings are perfectly slick. Same limitation discussed above applies to the pitch-catch method. Note that the disclosure of U.S. Pat. Application Publication No. 2004/0095847 is incorporated herein in its entirety by reference thereto.
U.S. Pat. No. 6,995,500 (Yogeswaren/Pathfinder, 2003) discloses 1-3 piezocomposite application to downhole pulse-echo measurement taking advantage of increased sensitivity thanks to acoustic impedance coupling. The reference also discloses exemplary of 3 transducer mounting design on a tool.
U.S. Pat. Application Publication No. 2009/0213690 (Steinsiek et al/Baker Hughes Incorporated, 2009) discloses 1-3 piezocomposite application to downhole pulse-echo caliper measurement similar to the foregoing U.S. Pat. No. 6,995,500.
J. Market and T. J. Parker (Halliburton), “Reliable LWD Calliper Measurements”, SPE-146245-MS (2011) discloses four transducer mounting configuration for LWD tool, however does not include fluid acoustic velocity measurements. The disclosure of this document is incorporated herein in its entirety by reference thereto.
C. Maeso and I. Tribe (Schlumberger), “Hole Shape from Ultrasonic Calipers and Density While Drilling—A Tool for Drillers”, SPE-71395-MS (2001) shows an example of application of LWD caliper measurements and how mud acoustic velocity is derived at the time. The disclosure of this document is incorporated herein in its entirety by reference thereto.
However, there is no document that discloses reliable and robust downhole caliper using real-time fluid acoustic slowness or velocity measurements as disclosed below.